https://github.com/nm-l2tp/network-manager-l2tp
https://github.com/libreswan/libreswan
sudo apt-get install build-essential intltool libgtk-3-dev libsecret-1-dev
sudo apt-get -t stretch install xl2tpd ppp-dev libnm-gtk-dev libnma-dev libnm-glib-vpn-dev libnl-3-200 libnl-genl-3-200 libnl-route-3-200
git clone https://github.com/nm-l2tp/network-manager-l2tp.git
cd network-manager-l2tp
git checkout 1.2.2
./autogen.sh
./configure \
--disable-static --prefix=/usr \
--sysconfdir=/etc --libdir=/usr/lib/x86_64-linux-gnu \
--libexecdir=/usr/lib/NetworkManager \
--localstatedir=/var \
--with-pppd-plugin-dir=/usr/lib/pppd/2.4.7
make
sudo make install
sudo reboot